1. Technical Field
The present invention relates generally to high-performance, fault-tolerant HTTP, streaming media and applications delivery in a content delivery network (CDN).
2. Description of the Related Art
It is well-known to deliver HTTP and streaming media using a content delivery network (CDN). A CDN is a network of geographically distributed content delivery nodes that are arranged for efficient delivery of digital content (e.g., Web content, streaming media and applications) on behalf of third party content providers. A request from a requesting end user for given content is directed to a “best” replica, where “best” usually means that the item is served to the client quickly compared to the time it would take to fetch it from the content provider origin server. An entity that provides a CDN is sometimes referred to as a content delivery network service provider or CDNSP.
Typically, a CDN is implemented as a combination of a content delivery infrastructure, a request-routing mechanism, and a distribution infrastructure. The content delivery infrastructure usually comprises a set of “surrogate” origin servers that are located at strategic locations (e.g., Internet network access points, Internet Points of Presence, and the like) for delivering copies of content to requesting end users. The request-routing mechanism allocates servers in the content delivery infrastructure to requesting clients in a way that, for web content delivery, minimizes a given client's response time and, for streaming media delivery, provides for the highest quality. The distribution infrastructure consists of on-demand or push-based mechanisms that move content from the origin server to the surrogates. An effective CDN serves frequently-accessed content from a surrogate that is optimal for a given requesting client. In a typical CDN, a single service provider operates the request-routers, the surrogates, and the content distributors. In addition, that service provider establishes business relationships with content publishers and acts on behalf of their origin server sites to provide a distributed delivery system. A commercial CDN service that provides web content and media streaming is provided by Akamai Technologies, Inc. of Cambridge, Mass.
A typical CDN edge server includes commodity hardware, an operating system such as Linux, a TCP/IP connection manager, a cache, and one or more applications that provide various functions such as cache management, logging, and other control routines that facilitate the content delivery techniques implemented by the CDNSP at the server. In an illustrative case, the operating system kernel is Linux-based and tracks and provides access to per session and aggregate TCP/IP information, such as per-system number of packets, bytes sent and received, number of retransmits, and the like. The TCP connection information that is available from monitoring the operating system kernel has not been fully mined for its potential value, especially to CDN service providers. TCP stream state data, however, generates implicit information about the state of the network. Thus, for example, packet retransmissions can indicate congestion within the network. An estimated round-trip-time (RTT) derived from TCP connection information indicates latency to a remote host. Early FIN message receipt can indicate a dropped connection. A lower window size than usual can indicate instability in topological path. Each session's overall and smaller time-scale throughput is one of the best measures of actual end-user performance.
It would be desirable to be able to use edge server CDN statistics in other CDN control processes.